1. Field of the Invention
This invention relates to oil and gas drilling equipment and more specifically relates to a mechanical setting tool apparatus commonly used with a whipstock assembly.
2. Background
It is often desirable to sidetrack (deviate) existing well boreholes for various reasons in producing more economical well bores. It is well known in the industry that whipstocks are used in drilling to direct or deviate a drill bit at an angle from a borehole. The borehole can be cased (lined with pipe casing) or uncased (no pipe casing). More often than not the previously bored hole is cased.
For a cased borehole, a drilling operator will set a cement plug in the borehole that is at least 100 feet deep followed by a packer or bridge plug. A packer may or may not be a complete seal above the cement plug depending upon the circumstances. A bridge plug is a wire line sealing device which is set three to five feet above the casing collar (or joint) near the required point that deviation of the borehole is needed. Of course, wire lines are used with packers as well for orienting whipstocks subsequently tripped into the borehole. The position of the packer or bridge plug and the whipstock is critical because the deviated borehole must not penetrate the casing at or near a casing collar (or joint). The whipstock is traditionally set several feet above the packer or bridge plug. Great care is exercised to coordinate wire line and pipe measurements to assure that the whipstock is clear of the casing collar.
Typically, the complete downhole assembly consists of a whipstock attached to some form of packer mechanism. Presently, there are two conventional whipstock types available. The first type combines a packer with attached whipstock positioned above the packer and the second is a single whipstock assembly with a plunger sticking out the bottom of the downhole tool. The whipstock is the actual oil tool that causes a drill bit to deviate from the original borehole. The packer or setting tool on the first type is another oil tool that holds the whipstock in place once the whipstock has been set in the cased borehole at the desired angle orientation.
On the second type, the plunger releases spring loaded slips when the tool is set down on the packer or bridge plug that is strategically positioned in the cased borehole. The slips hold the tool in place once they are forced against the casing by the released spring. The bottom trip device operates primarily in a cased borehole and it has problems because it only has a single slip or wedge to secure the whipstock in place which may not grip sufficiently to prevent movement of the whip under operating conditions.
A typical whipstock is a triangular shaped tool about 10 to 12 feet long. It is slightly less in diameter than the inside diameter of the pipe casing at its bottom and ramps upwardly to infinity at its top. The back of the tool usually rests against the pipe casing. The tool face is cup shaped or concave in appearance and guides the sidetracking borehole drilling equipment off to the side of the pipe casing in the direction set by the orientation of the ramped tool face. The bottom or base of the whipstock is attached to the packer or setting tool.
A whipstock of the proper diameter is chosen for each cased borehole so that its bottom diameter matches the pipe casing and packer or setting tool. Its top end should match the inside diameter of the borehole casing so that the sidetracking drilling assembly smoothly transitions through a window previously cut into the pipe casing.
Mechanically set anchors typically utilized to support whipstocks have either a one slip holding mechanism or two fixed slips and one moving or activating slip. Often times the holding capabilities of these conventional devices is not enough to prevent slippage or movement during sidetrack drilling operations. Moreover, the foregoing anchors only have load carrying capability in compression since tensional loads will serve to release the slips from their grasp of the pipe casing. In other words, single slip mechanical set anchors do not provide any upward load capability and very little torque capacity.
In addition, these devices are somewhat disadvantaged in that, when they are released from the pipe casing, they will drag against the casing when they are tripped from the borehole because the spring force used to activate the slips is not released.